1. Field of the Invention
The invention relates to a pavement marker that reflects and/or transmits light to identify selected regions of a driving lane.
2. Description of the Related Art
Traffic safety engineers design roads to give drivers a limited and predictable range of visual cues in an effort to generate predictable responses to those cues. The visual cues relate primarily to the shapes, colors and locations of traffic control devices. Standards for traffic control devices are specified in the Manual of Uniform Traffic Control Devices (MUTCD). The colors employed most widely in traffic control devices are white, red, yellow, fluorescent yellow-green and fluorescent orange.
White traffic control devices typically are employed on the traffic lane markings to identify the right edge of a travel lane or the demarcation between two travel lanes that permit travel flow in the same direction. Yellow is a warning indicator and is employed in travel lane markings to identify a demarcation between opposite flows of traffic. Thus, the center lane of a two-lane road will have a yellow stripe while each pavement edge of the two-lane road will have a white stripe. Red is used when a driver is required to stop or yield. For example, stop signs and yield, signs include white lettering on a red background. Red reflectors also are used to indicate that a driver is traveling in the wrong direction or to mark dangerous structures that a driver must avoid. Fluorescent yellow-green has been adopted more recently by the Manual of Uniform Traffic Control Devices to identify school crossing zones. Orange is recognized by the Manual of Uniform Traffic Control Devices to identify construction zones. Thus, orange signs may be used to announce the presence of a construction zone or to guide drivers through a construction zone.
Highway engineers often utilize pavement markers to help control traffic. A typical pavement marker has a base that is mounted to a surface of a roadway or that is embedded into the surface of the roadway. The pavement marker may also include at least one resin panel designed and oriented to produce optical signals in response to ambient light during daylight hours or headlights at night. More particularly, some panels are translucent and generate internal reflection of most of the light that impinges upon a major surface of the panel. The internally reflected light is emitted from an edge of the panel and produces a visually apparent glow along the edge. Panels of this type can be oriented with a major surface aligned to receive a maximum amount of ambient light and with an edge facing toward the driver. These panels can be effective during daylight, but have little effect at night. Other panels are configured with a matrix of rear surfaces aligned to reflect light toward the source of the light within certain ranges of angles of incidence. Thus, light emitted from the vehicular headlight will pass through the front surface and will be reflected back toward the driver. These panels are effective at night, but have little effect during the day.
The panels of pavement markers that redirect and/or reflect light may include a dye, pigment or colorant that will affect the color of the signal directed towards the driver. For example, a substantially transparent resin will reflect and/or transmit light that includes substantially the entire visible spectrum and will be perceived as a white signal. Transparent reflectors often are incorporated into pavement markers disposed along the shoulder of a road and are substantially coincident with a painted white line along the shoulder of the road. Thus, the reflected light will be perceived as a white signal and will supplement the white signal defined by the white line painted adjacent the right edge of the pavement. Resin panels that are dyed or colored yellow can be incorporated into pavement markers along the left edge of a one-way road and/or to indicate a demarcation between two oppositely flowing lanes of traffic. Similarly, red-dyed resin is used in reflectors that instruct a driver to stop or yield.
Some pavement markers include translucent or opaque panels with a fluorescent colorant. The fluorescent materials are excited in response to light energy impinging thereon and emit photons. Photons emitted from an opaque fluorescent material can be observed by a viewer spaced considerably from the opaque fluorescent material. Photons emitted by a translucent fluorescent material can be emitted from the edge to produce the above-described edge glow. Other panels have a fluorescent colorant and the above-described matrix of rear reflective surfaces. Thus the fluorescent light will be reflected back toward a driver. Fluorescent colorants can be selected to produce a fluorescent yellow-green optical signal in a school zone or fluorescent orange optical signal in a construction zone.
Some pavement markers are required primarily for their nighttime signal, such as those that mark the lane lines. Others are required primarily for a daytime signal, such as those used in a school zone. Many construction projects require traffic to be diverted both during the day and at night while a repair is being completed. For example, roadway resurfacing projects typically require at least one lane of a road to be closed while a section of roadway is removed and replaced. Similar lane-by-lane closures occur when a bridge surface must be replaced. A pavement marker used in these situations must be effective in both the day and might.
The assignee of the subject invention also owns U.S. Pat. No. 6,511,256 which covers a pavement marker with improved daytime visibility and fluorescent durability. The pavement marker includes a base, a top panel for producing a daytime edge glow signal and a front panel for producing a reflective nighttime signal. U.S. Pat. No. 6,511,256 discloses a specific fluorescent orange colorant in an acrylic resin to provide a daytime signal for identifying a construction zone.
A top panel and a retroreflective front panel must be secured to the base of the pavement marker in a manner that will withstand frequent impact by vehicular tires. The attachment of the panels to the base has been achieved by mechanical fasteners, adhesives and by ultrasonic welding.
The pavement marker disclosed in the above-referenced U.S. Pat. No. 6,511,256 offers many desirable features relating to improved daytime visibility and the durability of the fluorescents. However, a pavement marker that can provide both a strong nighttime signal and an even stronger daytime signal, such as a signal indicative of a construction zone or school zone, would be received favorably.